Solution polymerization in the presence of a salt of peroxydisulfuric acid with an organic nitrogenous base

ABSTRACT

POLYMERIZATION OF OLEFINICALLY UNSATURATED ORGANIC COMPOUNDS, PARTICULARLY MIXTURES OF MONOMERS CONTAINING AT LEAST 80% BY WEIGHT OF ACRYLONITRILE, IN AN ORGANIC SOLVENT WITH A SALT OF PEROXYDISULFURIC ACID WHICH IS SOLUBLE IN THE SAID SOLVENT. PALE TO COLORLESS AND CLEAR POLYMERS ARE OBTAINED.

United States Patent U.S. Cl. 260-855 17 Claims ABSTRACT OF THEDISCLOSURE Polymerization of olefinically unsaturated organic compounds,particularly mixtures of monomers containing at least 80% by weight ofacrylonitrile, in an organic solvent with a salt of peroxydisulfuricacid which is soluble in the said solvent. Pale to colorless and clearpolymers are obtained.

This invention relates to a process for the polymerization ofolefinically unsaturated organic compounds in organic solvents.

It is known that olefinically unsaturated organic compounds can bepolymerized in organic solvents with free radical forming initiatorssuch as azoisobutyronitrile or peroxy compounds. These initiators arenot satisfactory in every respect because they often cause troublesomediscoloration of the polymers or their solutions. Initiators such as thesodium, potassium or ammonium salts of peroxydisulfuric acid which donot exhibit this disadvantage are not suitable for polymerization inorganic solvents because of their sparing solubility.

It is an object of this invention to provide a method of polymerizingolefinically unsaturated organic compounds, particularly acrylonitrile,to form pale to colorless and clear polymers. These and other objectswhich will appear from the following description are achieved by thisinvention.

In accordance with the invention a method of polymerizing olefinicallyunsaturated organic compounds in organic solvents with polymerizationinitiators comprises using as the initiator a salt of peroxydisulfuricacid which is soluble in the said initiator.

Examples of olefinically unsaturated organic compounds which can bepolymerized according to the invention are D li-olefinically unsaturatedcarboxylic acids having three to five carbon atoms such as acrylic acid,methacrylic acid or crotonic acid, or their derivatives such as esterswith monohydroxyl compounds having one to eighteen carbon atoms such asmethyl acrylate, butyl acrylate or 2-ethylhexyl acrylate or amides ornitriles of these acids, and also viuylaromatics such as styrene, orvinyl esters of monocarboxylic acids such as vinyl acetate or vinylpropionate, and also vinyl halides such as vinyl chloride or vinylidenechloride, further olefinically unsaturated sulfonic acids such asvinylsulfonic acid, 3-sulfopropyl methacrylate, or olefinicallyunsaturated basic nitrogen compounds such as vinylpyridines orZ-diethylaminoethyl acrylate, or mixtures of the said monomers.

Acrylonitrile or a mixture of monomers containing more than 80% byweight of acrylonitrile can be polymerized particularly advantageouslyaccording to the invention. The monomers other than acrylonitrile areparticularly those specified above.

Examples of organic solvents in which the polymerization may be carriedout are: alcohols, ketones, or (particularly in the polymerization ofacrylonitrile or mixtures of monomers containing mainly acrylonitrile)dimethylformamide, dimethylacetamide, butyrolactone, ethylene carbonate,dimethyl sulfoxide or tetramethylenesulfone.

The soluble salts of peroxydisulfuric acid may be those which aresoluble in organic solvents, particularly salts of peroxydisulfuric acidwith organic bases containing nitrogen. Suitable bases include primary,secondarv, tertiary and quaternary nitrogen bases having aliphaticlinear or branched radicals having one to thirty, particularly two toeight, carbon atoms, cycloaliphatic radicals having five to ten ringcarbon atoms or araliphatic radicals having six to ten ring carbonatoms. Hydrocarbon radicals are particularly suitable as radicals, butthese radicals may also contain substituents in the chain, such ashalogen, COOR, CO-NH or CONR or heteroatoms such as oxygen or nitrogenatoms. Suitable radicals are for example methyl, ethyl, n-propyl, n-,isoor t-butyl, nhexyl, n-lauryl, cyclohexyl, benzyl, 3-methoxypropyl orZ-hydroethyl. Radicals present on a nitrogen atom may be identical ordifferent. Basic heterocycles such as morpholine, pyrrolidine, pyridineor substituted pyridines are also suitable as bases. It is advantageousto use a salt of peroxydisulfuric acid with two equivalents of base.Generally organic bases are chosen whose peroxydisulfates are soluble inthe solvent used and which are not oxidized by the peroxydisulfuricacid; this can be ascertained by a preliminary experiment withoutdifficulty.

The soluble salt of peroxydisulfuric acid is added in solid or dissolvedform to the polymerization mixture in an amount of from 0.01 to 2%,advantageously from 0.03 to 1.2% and particularly from 0.05 to 0.8%, byweight with reference to the monomers.

The salts of peroxydisulfuric acid are generally prepared by reactingaqueous or alcoholic solutions of the abovementioned organic bases withaqueous solutions of peroxydisulfuric acid at temperatures of from about0 to 20 C., the solutions of the bases generally being placed in thereactor first. In some cases, such as when benzylamine is used, theperoxydisulfate crystallizes out from the aqueous or aqueous alcoholicsolution. If this is not the case, the solution may be concentrated invacuo at from 15 to 20 C. The salts of peroxydisulfuric acid aregenerally prepared with 2 equivalents of base. A temperature of lessthan 25 C. is advantageously chosen for storing the salts.

It has proved to be advantageously to prepare peroxydisulfuric acid fromits sodium, potassium or ammonium salts in aqueous solutions by means ofacid ion exchangers. Generally from 5 to 40% solutions are prepared. Itis recommended that low temperatures, such as 0 to 5 C., should be usedand that the peroxydisulfuric acid should be reacted without undue delaybecause aqueous solutions of this acid do not generally have adequatestability.

Polymerization may be carried out in the conventional way inconventional apparatus. It may be carried out continuously or inbatches. It is generally carried out at from 35 to 100 C., particularlyat from 50 to C., advantageously under a protective gas. Polymerizationis usually carried out in from 20 to 40% solution.

The polymers prepared according to the invention have many applications.For example the acrylonitrile polymers are preferably used for theproduction of shaped articles, particularly filaments, threads orfibers, with or without the use of conventional additives such asstabilizers, antistatic agents or dyes. Direct processing of theacrylonitrile polymer solutions obtained by polymerization, for exampleby dry or wet spinning without previous isolation of the polymer, isadvantageous.

Pale to colorless and clear polymer solutions are obtained in theprocess according to the invention. This is particularly surprising inthe production of acrylonitrile polymers because in this casediscoloration very readily takes place. The acrylonitrile polymersobtained have molecular weights which are well suited to the productionof filaments and threads. Polymers having K values of from 80 to 95(measured according to the formula of H. Fikentscher, Cellulosechemie,13, 58 (1932)) can be readily obtained. Shaped articles prepared fromthe polymers according to this invention have a particularly high degreeof whiteness.

It is an advantage that even in the polymerization of acrylonitrile ormixtures of monomers containing mainly acrylonitrile indimethylforrnamide (in which discoloration takes place particularlyreadily) pale to practically colorless polymer solutions which can beprocessed into shaped articles having a very high degree of whitenessare obtained when using the initiators according to this invention.

The invention is illustrated by the following examples. The parts andpercentages specified in the examples are by weight.

EXAMPLE 1 Parts Acrylonitrile 27.7 Methyl acrylate 2.0 Sodiummethacroyloxypropyl sulfonate 0.3 Dimethylformamide 70.0Bis-(n-butylammonium)-peroxydisulfate 0.106

The mixture is stirred at 45 C. under nitrogen for twenty hours. At aconversion of 80%, the K value of the practically colorless, clearpolymer is 85 (according to Fikentscher, loc. cit.).

EXAMPLE 2 Parts Acrylonitrile 27.7 Methyl acrylate 2.0 Sodiummethacroyloxypropylsulfonate 0.3 Dimethylformamide 70.0Bis-(benzylammonium)-peroxydisulfate 0.13

A practically colorless, clear polymer solution is obtained in ten hoursat temperatures of from 40 to 50 C. The conversion is 70% and the Kvalue (according to Fikentscher) of the polymer is 95. The polymersolution may be readily processed into filaments and threads having ahigh degree of whiteness by wet or dry spinning.

If the experiment is repeated with potassium peroxydisulfate instead ofbis-(benzylammonium)-peroxy disulfate, a cloudy polymer solution isobtained which has to be filtered before it is used for spinning.

EXAMPLES 3-11 In accordance with Example 1, acryonitrile and the saidcomonomers are polymerized with the peroxydisulfates of the table at 50C., l millimole of the peroxydisulfate being used for 100 grams ofmonomer. The results are shown in the table. All solutions arepractically colorless and capable of being processed into filaments andthreads having a high degree of whiteness by wet or dry spinning.

We claim:

1. In a process for the solution polymerization of at least oneolefinically unsaturated organic monomer in anorganic solvent in thepresence of a small amount of a polymerization initiator, theimprovement which comprises using as the polymerization initiator a saltof peroxydisulfuric acid with an organic nitrogenous base, said saltbeing soluble in said organic solvent.

2. A process as claimed in claim 1 wherein said salt as thepolymerization initiator is used in an amount of 0.01 to 2% by weightwith reference to said at least one monomer.

3. A process as claimed in claim 1 wherein said salt as thepolymerization initiator is used in an amount of 0.05 to 0.8% by Weightwith reference to said at least one monomer.

4. In a process for the solution polymerization of acrylonitrile or amixture of olefinically unsaturated organic monomers containing at leastby Weight of acrylonitrile in an organic solvent in the presence of asmall amount of a polymerization initiator, the improvement whichcomprises using as the polymerization initiator about 0.01 to 2% byweight, with reference to the monomers, of a salt of peroxydisulfuricacid with an organic nitrogenous base, said salt being soluble in saidorganic solvent.

5. A process as claimed in claim 4 wherein said salt as thepolymerization initiator is used in an amount of 0.03 to 1.2% by weightwith reference to the monomers.

6. A process as claimed in claim 4 wherein said salt as thepolymerization initiator is used in an amount of 0.05 to 0.8% by weightwith reference to the monomers.

7. A process as claimed in claim 4 wherein said salt isbis-(n-butylamrnonium)-peroxydisulfate.

8. A process as claimed in claim 4 wherein said salt isbisbenzylammonium -peroxydisulfate.

9. A process as claimed in claim 4 wherein said salt isbis-(dimethylammonium)-peroxydisulfate.

10. A process as claimed in claim 4 wherein said salt isbis-(n-propylammonium)-peroxydisulfate.

11. A process as claimed in claim 4 wherein said salt is hisN-methyl-N-cyclohexylammonium-peroxydisulfate.

12. A process as claimed in claim 4 wherein said salt isbis-(tert.-butylammoniurn)-peroxydisulfate.

13. A process as claimed in claim 4 wherein said salt is his(tri-2-hydroxyethylammonium -peroxydisulfate.

14. A process as claimed in claim 4 wherein said salt isbis-(morpholino) -peroxydisulfate.

15. A process as claimed in claim 4 wherein said salt is bispyridinium-peroxydisulfate.

16. A process as claimed in claim 4 wherein said salt isbis-(pyrrolidinium)-peroxydisulfate.

17. A process as claimed in claim 4 wherein said salt is bis-N-methyl-N-benzylammonium -peroxydisulf ate.

References (Iited UNITED STATES PATENTS 3,060,157 10/1962 Goodman et al.26085.5 F 3,366,605 1/1968 Seiner 26085.5 F

HARRY WONG, 111., Primary Examiner US. Cl. X.R.

+53% UNITED STATES PATENT OFFEE CERTIFICATE OF CURECTEQN Patent No.3,654,571 Dated January 11, 1972 Inventofle) Heinz Pohlemann et a1 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

[- I u v n i w Column 1, line 4, NITROGENOUS ShOUld read NITROGENEOUSColumn 2, line 52', 'advantageously" should read. advantageous Column.in the table, example 7, "Bis-(tri-Q-hydroethylammonium)" should readBis-(tr'i-2-hydr-oxyethy1ammounium) line 17',

claim 1, "nitrogenous" should read nitr'ogeneous 'line 35, claim 4,"nitrogenous" should read nitrogeneous Signed and sealed this 22nd dayofAugust 1972.

*( SEAL) Attest;

EDWARD M.FLETCHER,JR. ROBERT GOT'.SCI-IALK Attesting OfficerCommissioner of Patents

